1. Field of the Invention
This invention relates to variable magnification lens systems and more particularly to the discrete variation of the focal length of a lens system.
2. Description of the Prior Art
Recently, the lens systems usable with the outside finder-equipped 35 m/m cameras have become very compact. However, these lens systems are generally of single focal lengths, or are single lenses. At present, there are a few variable focus or zoom lens systems. But, these zoom lens systems lack compactness, taking so large a bulk and size as to be equal to that of an equivalent lens used in the TTL type single lens reflex cameras. Compactness of the zoom lens systems for use in the outside finder 35 m/m cameras is very difficult to achieve, as far as the zooming method which is generally accepted in the prior art is concerned.
In the art of 35 m/m cameras, it has been proposed to employ a method of discretely varying the focal length as the zooming method, with an advantage that a compactness of the lens system can be facilitated. In U.S. Pat. No. 3,388,650, there is disclosed a method of varying the magnification by inserting a supplementary lens system into a space between the master lens system and the image plane, and by shifting the master lens as a whole.